Chemistry Lecture: Moles, Particles, and Avogadro's Number

hey guys hope you're well so this lesson we are going to talk about this formula over here so the N the small n stands for number of mole which we've looked at in previous lessons where we looked at this formula of uh here the mole is such a large or an important part of chemistry that you are going to see this in in many formulas okay the capital n stands for number of now it could be atoms or it could be particles or molecules depending on what we are looking at okay let's write that a little bit better it's the number of atoms or what could be particles or it could be molecules for example and then n a well it's n and then there's a little subscript over there which is an a this stands for Avogadro evergard Rose number this was a scientist okay now this number is a number that you will be given in your test for exams it is 6.02 so 6.02 multiplied by 10 and then the exponent is 23. okay that is a number that you're going to use quite a bit um but they will give that to you in your exams you know like a new exam they give you like a table where you've got all these constant values that will be given to you okay now I'm going to show you how to use this formula and remember that these formulas can be used in different ways so let's quickly make a triangle you see how this capital N is at the top so whenever we make a triangle and you know which triangles I'm talking about right you know like in electricity you've got the triangles that have like a um v i and a r or maybe in electricity we also have like a q i and a t and in one of the previous lessons with moles I showed you that there was m n n capital M so whenever we have a triangle it makes our life very easy to be able to use the formula in different ways so you see that this n is at the top so we put the N at the top and then this one we can just put over here and then this one we can just put over there and then from that you can work out different formulas so for example if you want to calculate let's say you want to calculate this one over here then because that one is at the top let's just highlight it quickly then you can see that these two at the bottom they are next to each other so you would multiply them so you would say n is equal to small n multiplied by Avogadro's Number okay now maybe you 'll to calculate this one maybe we already know what that one is but let's just say we needed to work that one out well that would actually never really ask us to do that so let's not worry about that one um and then let's say they asked you to calculate this one so then you would say n equals now this is at the top and this is at the bottom and then you would just be using the normal formula okay so let me show you some questions now now you don't need to memorize this triangle what will happen is that in an exam or test they will give you this formula that formula is given to you and then from that you can make a triangle because the number that's always the letter that's always at the top always goes at the top of the triangle and then you can just say n and n a and then you can make a triangle for yourself so the other question that says determine the number of mole let's rather say mole if you have 12.04 times 10 to the 23 particles so we can use this formula as it is we're trying to calculate the number of mole the number of particles that they have given us is this number over here so 12.04 times 10 to the 23 and then n a is Avogadro's number which is this number over here so you could just go say 6.02 times 10 to the 23 and then you could um if you had to calculate that you're going to end up with two mole so here's our next example and I would advise that you stay to the end of this lesson because I'm also going to be doing some really interesting things in this lesson I'm also going to be teaching you how to use this formula together with this formula so we're going to use both of these at the same time and I'm also going to be showing you questions where for example if you have calcium carbonate I'm going to ask you for example how many particles or molecules of calcium carbonate do we have and then I'm also going to say how many oxygen atoms do we have or something like that or how many carbons do we have so teachers like asking those so just stay to the end of this lesson where we're going to talk about all of those things so here it is determine the number of molecules in three mole of H2O okay so we know that n is stands for mole n is the number of for example atoms or molecules for example molecules and then n a is Avogadro's constant or Avogadro's number and that is the 6.02 times 10 to the 23. so they're saying determine the number of particles so they want us to work out n so you need to know how to rearrange this formula so I advise that you just remember this little triangle which I literally just made by looking at that I know that n is at the top so I put it at the top and then the other two just go down here okay so if you want to get this part by itself you are going to multiply these two parts together so that's going to be n multiplied by Avogadro is constant and so to work out the number of particles you're going to take the moles which is three and you're going to multiply that by the number of Will Avogadro's number sorry which is 6.02 times 10 to the 23 and if you calculate this you get 1.806 multiplied by 10 to the power of 24 molecules so here's a pretty cool question it says determine the number of molecules in 36 grams of H2O now if we just try to use this formula we'll run into some problems because n is the number of mole um n is the number of particles or molecules or atoms and that's what they're asking us to find okay so this is the unknown we don't know what this one is now we know that n a is a constant 6.02 times 10 to the 23 so we don't know what this one is we do know what this one is but we don't know what this one is so you see we have two unknowns so that's a bit of a problem but then we know from previous lessons that there's also this formula that we could use so we know that the small m is the given Mass measured in grams and then the capital M is the molar mass on the periodic table and that's measured in grams per mole so what we could do is we could first go and use this formula to calculate the number of moles and once we have the number of moles then we can carry on with this formula so we could say that n is equal to 36 divided by now to work out the molar mass of H2O we're just going to go into our periodic table we can see that there is two hydrogens so two hydrogens and one oxygen so to work out the mass you could say 2 times 1 because hydrogen has a mass of one plus one oxygen which has a mass of 16 and that's going to give us 18 grams per mole so then we could use 18 over there and then we could work out that we have two moles so we have two mole of H2O so two moles of H2O so now all of a sudden we have the moles of H2O and we have Avogadro's number and so what we're trying to calculate now is this one so if you just look at your triangle with um n at the top n and n a i put this one at the top because it's at the top over here and so what we're trying to calculate is this one so if we want this one over here then that means you need to multiply these two so we know that we can say n is equal to n multiplied by n a so n is equal to the number of moles which is 2 multiplied by Avogadro's number which is 6.02 times 10 to the 23 and if you had to work this out you end up with 1.204 times 10 to the power of 24 molecules of H2O of H2O the next part of this lesson is really important let's say we have a water let's say we have a water molecule now a water molecule is made up of two hydrogens and one oxygen it says yeah two hydrogens and one oxygen so if we have 10 water molecules tin water molecules okay so let's actually go draw 10 water molecules and one more okay so here we have 10 water molecules so can you see how many or how many oxygens do we have well if you had to go count all the oxygens there's two three four five six seven eight nine ten so there were 10 water molecules and can you see that in each water molecule there's one oxygen so that means we also have 10 oxygens so this means we have 10 oxygen atoms and how many hydrogens would that be well if you had to go count all the hydrogens um there's two hydrogens for every single water molecule so that means if you have to go count that all up you should end up with 20 hydrogen atoms so 20 hydrogen atoms and so if you had to go count all the atoms all together there should be a total of 30 atoms 30 atoms all together so we had 10 water molecules but that's a molecule but if you had to go count all the different atoms there was actually 30 different atoms so let's try something like this they tell us that we have five CO2 molecules Okay so we've got five CO2 molecules let's say a CO2 looks like that it's got one carbon and two oxygens okay so that's one CO2 molecule now we have five of those okay so there we've got five CO2 molecules now the first question says how many carbon atoms do we have well that's just going to be one two three four five five molecules and then in each one we have one carbon so that means we're gonna have five carbon atoms five carbon atoms the next question says how many oxygens now instead of having to draw this out can you see that the answer will be 10 because in each of them they are two oxygen atoms and we have five of these all together so if you have to go count it to one two three four five six seven eight nine ten so ten oxygen atoms and so all together we have 15 atoms now another way to do this is if you look at a CO2 molecule it's got three atoms can you see that there's three atoms now if you have five of those well what is five times three well that would be fifteen so that's where we have 15 atoms now we're going to start making it a little bit more challenging so here's a really good example it is that we have been given two mole of CaCO3 now remember mole is not the number of particles mole is just this one over here okay so the first question says determine the number of CaCO3 molecules okay so that's an easy question we'll just use this formula now remember that n is the mole capital N is the number of molecules or atoms depending on what they're talking about and then uh let's see n a is Avogadro's number and that is 6.02 times 10 to the 23. so it says determine the number of CaCO3 molecules okay so we can just say um so we take this formula but they want us to work out the number of molecules so if we make a triangle we know that this is at the top so it's like that so if you want to get this one by itself then you are going to end up multiplying these two at the bottom together and so that's going to be number of moles multiplied by Avogadro's number and so if you had to work this out and that is going to give us 1.204 times 10 to the power of 24 CaCO3 molecules now for the next questions we need to check this out carefully so in a CaCO3 molecule so you've got a calcium you've got a carbon and then you've got three oxygens okay this actually just draw it so let's say it is that for example so can you see that for every calcium carbonate molecule for every one calcium carbonate molecule there is one calcium can you see that inside here for every one calcium carbonate there's one calcium so we can say that the ratio is one to one so that means that the number of calcium atoms is going to be the same as the number of calcium carbonate and so that's going to be 1.204 times 10 to the 24. now for this question it says determine the number of carbon atoms now if you look inside here for every one calcium carbonate there is also only going to be one carbon so they are in a one to one ratio so that means that this would also be 1.204 times 2 into the 24. now here's where it gets interesting they say determine the number of oxygen atoms well in every one calcium carbonate molecule there is one two three oxygens so the ratio of calcium carbonate to oxygen is in a one to three ratio so the number of oxygens will actually be 1.204 times 10 to the 24 multiplied by three and that would give us 3.612 times 10 to the power of 24. let's do another example so this is quite a good question because it's going to actually test us on a few different things so here they say we have been given 36 grams of H2O the first question says determine the number of H2O molecules okay so we need to work out the number of molecules so that's this one now we know that Avogadro's number is 6.02 times 10 to the 23 so we know this one but we don't know the number of moles so well done if you thought about we possibly will probably have to use this formula and so guys the rain has just started pouring um outside my window it is pouring so nicely I love it oh it's so beautiful okay so [Music] um where was I okay yes so we're gonna have to use this formula and to use this formula remember that m is the given Mass which is the mass that they give you okay it's the given mass and it's measured in grams then you get capital M which is called molar mass and that's from your periodic table which is this thing over here by the way and then that's measured in grams per mole and then um okay so we're gonna go use this formula so we're going to say n is equal to 36 which is the given mass now to work out the molar mass of H2O you need to use your periodic table so we know that in a in a molecule of H2O there are two hydrogens so two hydrogen atoms plus one oxygen so if we're to go work out the mass of that it would be two multiplied by the mass of a hydrogen which is one plus one multiplied by the mass of an oxygen which is 16 and that would give you 18 grams per mole so that's your capital M so we can put that over there if you calculate that you end up with two mole now we know the number of moles so we can come back to this formula and we can work out the number of particles remember the number of particles and the number of moles are not the same thing number of moles is this number of particles is this and so now we need to use this formula and we need to calculate the capital N so remember that you could make a little triangle for yourself where the N is at the top so that's going to be like that and then like that and like that so if you need to calculate this part which is at the top then you end up saying um small n multiplied by we say these two multiplied together and so that's going to be like that and so that would be 2 for the number of moles multiplied by Avogadro's number which is 6.02 times 10 to the 23 and that'll give us 1.204 times 10 to the 24. so that would be the number of water well H2O molecules okay so that would be the answer for question a now if you look at a water molecule okay now a water molecule is H2O so it's got two hydrogens and one oxygen okay that's important that we understand that for the next questions so the next questions for question B it says determine the number of hydrogen atoms now can you see that for one water molecule there are um two hydrogens so for one water molecule there are two hydrogens so if we know the number of water molecules then we can work out the number of hydrogens by just multiplying by two so we could say 1.204 times 10 to the 24 multiplied by two and that would give 2.408 times 10 to the 24 so that would be the number of hydrogen atoms okay now for the last question it says determine the number of oxygens so can you see that in one water molecule the ratio of so if you have one water molecule then the number of oxygens is one so the ratio is one to one for one water molecule you have one oxygen so that means that the number of oxygens will be the same as the number of water molecules which would be um 1.204 times 10 to the 24.

hey guys hope you&#39;re well so this lesson we are going to talk about this formula over here so the N the small n stands for number of mole which we&#39;ve looked at in previous lessons where we looked at this formula of uh here the mole is such a large or an important part of chemistry that you are going to see this in in many formulas okay the capital n stands for number of now it could be atoms or it could be particles or molecules depending on what we are looking at okay let&#39;s write that a little bit better it&#39;s the number of atoms or what could be particles or it could be molecules for example and then n a well it&#39;s n and then there&#39;s a little subscript over there which is an a this stands for Avogadro evergard Rose number this was a scientist okay now this number is a number that you will be given in your test for exams it is 6.02 so 6.02 multiplied by 10 and then the exponent is 23. okay that is a number that you&#39;re going to use quite a bit um but they will give that to you in your exams you know like a new exam they give you like a table where you&#39;ve got all these constant values that will be given to you okay now I&#39;m going to show you how to use this formula and remember that these formulas can be used in different ways so let&#39;s quickly make a triangle you see how this capital N is at the top so whenever we make a triangle and you know which triangles I&#39;m talking about right you know like in electricity you&#39;ve got the triangles that have like a um v i and a r or maybe in electricity we also have like a q i and a t and in one of the previous lessons with moles I showed you that there was m n n capital M so whenever we have a triangle it makes our life very easy to be able to use the formula in different ways so you see that this n is at the top so we put the N at the top and then this one we can just put over here and then this one we can just put over there and then from that you can work out different formulas so for example if you want to calculate let&#39;s say you want to calculate this one over here then because that one is at the top let&#39;s just highlight it quickly then you can see that these two at the bottom they are next to each other so you would multiply them so you would say n is equal to small n multiplied by Avogadro&#39;s Number okay now maybe you &#39;ll to calculate this one maybe we already know what that one is but let&#39;s just say we needed to work that one out well that would actually never really ask us to do that so let&#39;s not worry about that one um and then let&#39;s say they asked you to calculate this one so then you would say n equals now this is at the top and this is at the bottom and then you would just be using the normal formula okay so let me show you some questions now now you don&#39;t need to memorize this triangle what will happen is that in an exam or test they will give you this formula that formula is given to you and then from that you can make a triangle because the number that&#39;s always the letter that&#39;s always at the top always goes at the top of the triangle and then you can just say n and n a and then you can make a triangle for yourself so the other question that says determine the number of mole let&#39;s rather say mole if you have 12.04 times 10 to the 23 particles so we can use this formula as it is we&#39;re trying to calculate the number of mole the number of particles that they have given us is this number over here so 12.04 times 10 to the 23 and then n a is Avogadro&#39;s number which is this number over here so you could just go say 6.02 times 10 to the 23 and then you could um if you had to calculate that you&#39;re going to end up with two mole so here&#39;s our next example and I would advise that you stay to the end of this lesson because I&#39;m also going to be doing some really interesting things in this lesson I&#39;m also going to be teaching you how to use this formula together with this formula so we&#39;re going to use both of these at the same time and I&#39;m also going to be showing you questions where for example if you have calcium carbonate I&#39;m going to ask you for example how many particles or molecules of calcium carbonate do we have and then I&#39;m also going to say how many oxygen atoms do we have or something like that or how many carbons do we have so teachers like asking those so just stay to the end of this lesson where we&#39;re going to talk about all of those things so here it is determine the number of molecules in three mole of H2O okay so we know that n is stands for mole n is the number of for example atoms or molecules for example molecules and then n a is Avogadro&#39;s constant or Avogadro&#39;s number and that is the 6.02 times 10 to the 23. so they&#39;re saying determine the number of particles so they want us to work out n so you need to know how to rearrange this formula so I advise that you just remember this little triangle which I literally just made by looking at that I know that n is at the top so I put it at the top and then the other two just go down here okay so if you want to get this part by itself you are going to multiply these two parts together so that&#39;s going to be n multiplied by Avogadro is constant and so to work out the number of particles you&#39;re going to take the moles which is three and you&#39;re going to multiply that by the number of Will Avogadro&#39;s number sorry which is 6.02 times 10 to the 23 and if you calculate this you get 1.806 multiplied by 10 to the power of 24 molecules so here&#39;s a pretty cool question it says determine the number of molecules in 36 grams of H2O now if we just try to use this formula we&#39;ll run into some problems because n is the number of mole um n is the number of particles or molecules or atoms and that&#39;s what they&#39;re asking us to find okay so this is the unknown we don&#39;t know what this one is now we know that n a is a constant 6.02 times 10 to the 23 so we don&#39;t know what this one is we do know what this one is but we don&#39;t know what this one is so you see we have two unknowns so that&#39;s a bit of a problem but then we know from previous lessons that there&#39;s also this formula that we could use so we know that the small m is the given Mass measured in grams and then the capital M is the molar mass on the periodic table and that&#39;s measured in grams per mole so what we could do is we could first go and use this formula to calculate the number of moles and once we have the number of moles then we can carry on with this formula so we could say that n is equal to 36 divided by now to work out the molar mass of H2O we&#39;re just going to go into our periodic table we can see that there is two hydrogens so two hydrogens and one oxygen so to work out the mass you could say 2 times 1 because hydrogen has a mass of one plus one oxygen which has a mass of 16 and that&#39;s going to give us 18 grams per mole so then we could use 18 over there and then we could work out that we have two moles so we have two mole of H2O so two moles of H2O so now all of a sudden we have the moles of H2O and we have Avogadro&#39;s number and so what we&#39;re trying to calculate now is this one so if you just look at your triangle with um n at the top n and n a i put this one at the top because it&#39;s at the top over here and so what we&#39;re trying to calculate is this one so if we want this one over here then that means you need to multiply these two so we know that we can say n is equal to n multiplied by n a so n is equal to the number of moles which is 2 multiplied by Avogadro&#39;s number which is 6.02 times 10 to the 23 and if you had to work this out you end up with 1.204 times 10 to the power of 24 molecules of H2O of H2O the next part of this lesson is really important let&#39;s say we have a water let&#39;s say we have a water molecule now a water molecule is made up of two hydrogens and one oxygen it says yeah two hydrogens and one oxygen so if we have 10 water molecules tin water molecules okay so let&#39;s actually go draw 10 water molecules and one more okay so here we have 10 water molecules so can you see how many or how many oxygens do we have well if you had to go count all the oxygens there&#39;s two three four five six seven eight nine ten so there were 10 water molecules and can you see that in each water molecule there&#39;s one oxygen so that means we also have 10 oxygens so this means we have 10 oxygen atoms and how many hydrogens would that be well if you had to go count all the hydrogens um there&#39;s two hydrogens for every single water molecule so that means if you have to go count that all up you should end up with 20 hydrogen atoms so 20 hydrogen atoms and so if you had to go count all the atoms all together there should be a total of 30 atoms 30 atoms all together so we had 10 water molecules but that&#39;s a molecule but if you had to go count all the different atoms there was actually 30 different atoms so let&#39;s try something like this they tell us that we have five CO2 molecules Okay so we&#39;ve got five CO2 molecules let&#39;s say a CO2 looks like that it&#39;s got one carbon and two oxygens okay so that&#39;s one CO2 molecule now we have five of those okay so there we&#39;ve got five CO2 molecules now the first question says how many carbon atoms do we have well that&#39;s just going to be one two three four five five molecules and then in each one we have one carbon so that means we&#39;re gonna have five carbon atoms five carbon atoms the next question says how many oxygens now instead of having to draw this out can you see that the answer will be 10 because in each of them they are two oxygen atoms and we have five of these all together so if you have to go count it to one two three four five six seven eight nine ten so ten oxygen atoms and so all together we have 15 atoms now another way to do this is if you look at a CO2 molecule it&#39;s got three atoms can you see that there&#39;s three atoms now if you have five of those well what is five times three well that would be fifteen so that&#39;s where we have 15 atoms now we&#39;re going to start making it a little bit more challenging so here&#39;s a really good example it is that we have been given two mole of CaCO3 now remember mole is not the number of particles mole is just this one over here okay so the first question says determine the number of CaCO3 molecules okay so that&#39;s an easy question we&#39;ll just use this formula now remember that n is the mole capital N is the number of molecules or atoms depending on what they&#39;re talking about and then uh let&#39;s see n a is Avogadro&#39;s number and that is 6.02 times 10 to the 23. so it says determine the number of CaCO3 molecules okay so we can just say um so we take this formula but they want us to work out the number of molecules so if we make a triangle we know that this is at the top so it&#39;s like that so if you want to get this one by itself then you are going to end up multiplying these two at the bottom together and so that&#39;s going to be number of moles multiplied by Avogadro&#39;s number and so if you had to work this out and that is going to give us 1.204 times 10 to the power of 24 CaCO3 molecules now for the next questions we need to check this out carefully so in a CaCO3 molecule so you&#39;ve got a calcium you&#39;ve got a carbon and then you&#39;ve got three oxygens okay this actually just draw it so let&#39;s say it is that for example so can you see that for every calcium carbonate molecule for every one calcium carbonate molecule there is one calcium can you see that inside here for every one calcium carbonate there&#39;s one calcium so we can say that the ratio is one to one so that means that the number of calcium atoms is going to be the same as the number of calcium carbonate and so that&#39;s going to be 1.204 times 10 to the 24. now for this question it says determine the number of carbon atoms now if you look inside here for every one calcium carbonate there is also only going to be one carbon so they are in a one to one ratio so that means that this would also be 1.204 times 2 into the 24. now here&#39;s where it gets interesting they say determine the number of oxygen atoms well in every one calcium carbonate molecule there is one two three oxygens so the ratio of calcium carbonate to oxygen is in a one to three ratio so the number of oxygens will actually be 1.204 times 10 to the 24 multiplied by three and that would give us 3.612 times 10 to the power of 24. let&#39;s do another example so this is quite a good question because it&#39;s going to actually test us on a few different things so here they say we have been given 36 grams of H2O the first question says determine the number of H2O molecules okay so we need to work out the number of molecules so that&#39;s this one now we know that Avogadro&#39;s number is 6.02 times 10 to the 23 so we know this one but we don&#39;t know the number of moles so well done if you thought about we possibly will probably have to use this formula and so guys the rain has just started pouring um outside my window it is pouring so nicely I love it oh it&#39;s so beautiful okay so [Music] um where was I okay yes so we&#39;re gonna have to use this formula and to use this formula remember that m is the given Mass which is the mass that they give you okay it&#39;s the given mass and it&#39;s measured in grams then you get capital M which is called molar mass and that&#39;s from your periodic table which is this thing over here by the way and then that&#39;s measured in grams per mole and then um okay so we&#39;re gonna go use this formula so we&#39;re going to say n is equal to 36 which is the given mass now to work out the molar mass of H2O you need to use your periodic table so we know that in a in a molecule of H2O there are two hydrogens so two hydrogen atoms plus one oxygen so if we&#39;re to go work out the mass of that it would be two multiplied by the mass of a hydrogen which is one plus one multiplied by the mass of an oxygen which is 16 and that would give you 18 grams per mole so that&#39;s your capital M so we can put that over there if you calculate that you end up with two mole now we know the number of moles so we can come back to this formula and we can work out the number of particles remember the number of particles and the number of moles are not the same thing number of moles is this number of particles is this and so now we need to use this formula and we need to calculate the capital N so remember that you could make a little triangle for yourself where the N is at the top so that&#39;s going to be like that and then like that and like that so if you need to calculate this part which is at the top then you end up saying um small n multiplied by we say these two multiplied together and so that&#39;s going to be like that and so that would be 2 for the number of moles multiplied by Avogadro&#39;s number which is 6.02 times 10 to the 23 and that&#39;ll give us 1.204 times 10 to the 24. so that would be the number of water well H2O molecules okay so that would be the answer for question a now if you look at a water molecule okay now a water molecule is H2O so it&#39;s got two hydrogens and one oxygen okay that&#39;s important that we understand that for the next questions so the next questions for question B it says determine the number of hydrogen atoms now can you see that for one water molecule there are um two hydrogens so for one water molecule there are two hydrogens so if we know the number of water molecules then we can work out the number of hydrogens by just multiplying by two so we could say 1.204 times 10 to the 24 multiplied by two and that would give 2.408 times 10 to the 24 so that would be the number of hydrogen atoms okay now for the last question it says determine the number of oxygens so can you see that in one water molecule the ratio of so if you have one water molecule then the number of oxygens is one so the ratio is one to one for one water molecule you have one oxygen so that means that the number of oxygens will be the same as the number of water molecules which would be um 1.204 times 10 to the 24.

Transcript for:Chemistry Lecture: Moles, Particles, and Avogadro's Number

Transcript for:
Chemistry Lecture: Moles, Particles, and Avogadro's Number